1. Field of the Invention
The present invention relates to an electronic flash device and a camera and, more particularly, to an electronic flash device which can perform previous light emission for red-eye reduction and a camera.
2. Description of the Related Art
In recent years, with an increase in resolution of an image pickup device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) image sensor, the demand for digital camera has been rapidly increasing. As digital cameras of this type, a large number of products which can photograph not only still images but also videos are commercialized.
In a digital camera of this type, in general, when an object to be photographed is dark, the object is photographed such that flash light is irradiated on the object. At this time, light reflected from the retina of a pupil is reddish. As a result, a so-called red-eye phenomenon in which the pupils of a person are photographed as red pupils may occur. Conventionally, various technologies for reducing red-eye phenomena have been disclosed. As a typical technology for reducing a red-eye phenomenon, a technology (for example, technology described in Japanese Patent Application Laid-Open (JP-A) No. 2001-174884) in which a flash is preliminarily fired (so-called pre-emission) to constrict pupils and mainly fired for photographing after the pupils are constricted is widely known.
FIG. 5 shows an electric configuration of a conventional digital camera which performs the preliminary emission. The digital camera shown in FIG. 5 includes: an image pickup system constituted by a CCD for picking an object image, an analog signal processing unit for performing various pieces of analog signal processing to analog image information obtained by the CCD, an ADC (analog/digital converter) for converting the analog image information into digital image information, and a digital signal processing unit for performing various pieces of digital signal processing to the digital image information, a CPU (Central Processing Unit) for controlling the entire operation of digital camera 10, and an electronic flash device for irradiating auxiliary light to an object if necessary in a photographing operation.
Although not shown, a digital camera of this type generally includes a display system for displaying a picked image, a recording medium for recording image information obtained by image pickup, and the like.
In general, such a digital camera, as shown in FIG. 5, comprises a timing generator for generating a timing signal for driving a CCD, an analog signal processing unit, an ADC, and the like under the control of a CPU to supply the timing signal to the respective components. A main emission signal for causing a light-emitting tube included in an electronic flash to perform main emission is generated by the timing generator. However, a preliminary emission signal for causing the light-emitting tube to preliminarily emit light is generated by a process performed by software in the CPU.
In the above conventional technology for performing preliminary emission, preliminary emission is generally performed regardless of an operation timing of a CCD. For this reason, when preliminary emission is performed in photographing of a video and in a period of exposure performed by the CCD, only a frame corresponding to the exposure period is brighter than other frames. As a result, a display screen of the video disadvantageously flickers.
When a CCD is used as an image pickup device, as an example, as shown in FIG. 6, image signals of frames are sequentially output from the CCD at timings synchronous with a vertical synchronous signal VD. In this case, a period except for a period in which an overflow drain signal OFD representing a timing at which excess charges are drained by an overflow drain arranged in the CCD is input to the CCD is almost equal to an exposure period of the CCD. However, a preliminary emission signal YS representing a timing of preliminary emission in the period is output toward a light-emitting tube, an image signal obtained by an image pickup operation performed in this period has a luminance which is considerably higher than that of an image signal obtained in another period. Therefore, when a video is displayed by using the image signal obtained as described above, the display image flickers.
Therefore, as conventional technologies, the following technologies are known. That is, as shown in FIG. 6, the display of an immediately previous frame is frozen as the display of a frame corresponding to a period of preliminary emission, or the display of the corresponding frame is blacked out (inky black).
However, by the technology for freezing a display screen or the technology -for blacking out a display screen, an actual image of a frame corresponding to a period of preliminary emission is not displayed. For this reason, a video is not smoothly displayed.
As is described with reference to FIG. 5, in a conventional digital camera which can perform preliminary emission, the preliminary emission signal is generally generated by a process performed by software in a CPU. For this reason, a load of processing on the CPU disadvantageously increases in comparison with a case in which preliminary emission is not performed.